This invention relates a driveshaft supporting device for a marine propulsion unit and more particularly to an improved arrangement for preloading the thrust bearing in a driveshaft support so as to avoid noise.
As is well known, marine outward drives normally incorporate a driveshaft that is supported within an outer housing for rotation about a vertically extending axis. The rotational support for the driveshaft includes a thrust bearing for taking the thrust loading on the driveshaft. However, the speed of rotation of the driveshaft frequently is changed and furthermore, the propeller thrust or the driving thrust at the lower end of the driveshaft may fluctuate so as to cause varying forces to be exerted upon the driveshaft in axial directions. As a result, the driveshaft tends to move vertically relative to the thrust bearing under such changes in loading and this movement will cause noise to be generated as clearances are taken up.
It has, therefore, been proposed to provide a biasing arrangement for preloading the thrust bearing. Such biasing arrangement of the type previously proposed employ a coil spring which encircles the driveshaft and bears against it and its supporting housing so as to preload the thrust bearing. However, because of the extremely compact nature of these outboard drives it is very difficult to provide a coil spring that will have sufficient strength so as to maintain the necessary preload to avoid noise.
It should also be born in mind that it is desirable to position the spring above the water level so that if it adds any size to the driveshaft housing this size increase will occur above the water line so as to reduce the flow resistance. However, the previously proposed arrangements have not, for the reasons already noted, afforded sufficient preloading on the thrust bearing so as to avoid noise and wear on the thrust bearing due to the fluctuations in loading.
It is, therefore, a principle object of this invention to provide an improved driveshaft support for a marine outboard drive.
It is a further object of this invention to provide an improved driveshaft support for a marine outboard drive in which adequate biasing springs may be incorporated so as to preload the thrust bearing.
It is yet another object of the invention to provide an arrangement for preloading the thrust bearing in a marine outboard drive to avoid noise.